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NEW YORK — The symptoms of Parkinson's disease that all but ended Michael J. Fox's acting career are making him a powerfully vulnerable campaign pitchman for five Democrats who support stem cell research.

In the McCaskill ad, which has been viewed by more than 1 million people on YouTube.com, Fox tells voters, "What you do in Missouri matters to millions of Americans. Americans like me."

He also was planning to appear at events for Sen. Robert Menendez of New Jersey and Tammy Duckworth, a candidate for Congress from Illinois.

Potential tie-breaker?
Celebrities have a long history of supporting political candidates. But there's no question that Fox, who campaigned for John Kerry in the 2004 presidential race, is uniquely suited as a spokesman for embryonic stem cell research, which some scientists believe could aid in discovering treatments or cures to Parkinson's and other diseases.

Fox's ads may even turn the close Senate race between McCaskill and Republican incumbent Jim Talent in Missouri, said Larry Sabato, a professor at the University of Virginia and director of its Center for Politics. He described the spots as "very powerful."
2006 key races

"If a tiny ad can change votes, this one ought to," said Sabato. "This is real. He's not playing a guy with Parkinson's - he IS a guy with Parkinson's."

Parkinson's disease is a chronic, progressive disorder of the central nervous system that leaves patients increasingly unable to control their movements. In his ads, Fox shows a remarkable nakedness that recalls Dick Clark's appearance last Dec. 31 on ABC's "New Year's Rockin' Eve," displaying the effects of his debilitating stroke a year prior.

Parkinson's victim
Fox was diagnosed with Parkinson's in 1991 and revealed his condition publicly in 1998. In 2000, the "Spin City" and "Back to the Future" star quit full-time acting because of his symptoms and founded the Michael J. Fox Foundation for Parkinson's Research, which has raised millions of dollars.

He has since acted sporadically in smaller roles, such as in a several-episode guest appearance earlier this year on ABC's "Boston Legal," playing a business tycoon with cancer. For that role and others, Fox generally has sought to control his movements. He told The Associated Press in January that one long scene was physically taxing and that because of his illness, he "can't show up with a game plan."

In the same interview, Fox said he felt sympathy for Clark, who received a mixed reaction for his New Year's appearance.

Similarly, some have criticized Fox's ads as exploitive. Conservative radio commentator Rush Limbaugh claimed Fox was "either off his medication or acting" during the ad.

Others defend Fox's aggressive campaigning for a Parkinson's cure. Dr. John Boockvar, a neurosurgeon and assistant professor at Weill Cornell Medical Center at New York's Presbyterian Hospital, called Limbaugh's claim that Fox was acting "ludicrous." Boockvar said those with Parkinson's have "on" and "off" spells.

"If there is one single disease that has the highest potential for benefit from stem cell research," Boockwar said Tuesday, "it's Parkinson's."

Copyright 2006 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.